EARTH

EARTH
From space our home planet, Earth, appears to be mainly blue in colour. This is because of the colour of the oceans which cover over two-thirds of its surface. The land areas, or continents, cover less than a third. The layer of air above the surface is thin, but makes life on Earth possible.

What causes day and night?

Almost every place on Earth has a time when it is light(day), followed by a time when it is dark(night). Day and night come about because Earth spins round in space, and different parts of its surface face the Sun. It is daytime when a place is on the side of Earth facing the Sun. It becomes night when the place is on the side of Earth facing away from the Sun.

What makes Earth different?

A number of things make Earth different from other planets. It is covered with great oceans of water, and its atmosphere contains lots of oxygen. The atmosphere also acts like a blanket, holding in enough of the Sun’s heat to keep Earth at comfortable temperature. The water, the oxygen and the temperature make Earth a suitable place for living things - at least one-and-a-half million different kinds of plants and animals.

How has Earth changed?

Earth formed about 4,600 million years ago when bits of matter in space come together. At first Earth was a great molten ball. It gradually cooled and the atmosphere and oceans eventually formed. In time, it changed into the world we know today, made up of layers of rock with a metal core. Our world is still changing. Currents in the rocks beneath the crust widening the oceans, and driving the continents further apart.

What causes the seasons?

The changes in weather that we call the seasons happen because of the way Earth’s axis is tilted in space. Because of this tilt, a place leans more towards the Sun and is warmer at some times of the year than at others. It is this that causes the changing seasons. The place tilted towards the Sun has summer, while the place leaning away has winter.

EARTH DATA

Diameter at equator : 12,756 km

Average distance from the sun : 149.6 million km

Turns on axis : 23 hours 56 minutes

Year length : 365.25 days

Surface temperature : -89°C to 58°C

Satellites : 1(the Moon)

NEPTUNE AND PLUTO

NEPTUNE AND PLUTO

Neptune and Pluto were the last planets to be discovered. They lie thousands of millions kilometres away from Earth, at the edge of the Solar System. Neptune is a gas giant, very like Uranus. Pluto is a tiny ice ball, smaller than our own Moon.

Why is Neptune blue?

Neptune is a lovely blue colour, rather like Earth. This colour comes about because the atmosphere contains a gas called methane. Methane absorbs the red colours in sunlight, and makes the light coming from Neptune’s atmosphere appear blue. Dark spots that sometimes appear in Neptune’s atmosphere are violent storms.

Does Neptune have moons?

Through a telescope, we can see two moons circling around Neptune – Triton and Nereid. When Voyager 2 visited the planet, it found six more. One, Proteus, was slightly bigger than Nereid, but the others were tiny. Triton is by far the biggest moon, measuring some 2,700 kilometres across. Unusually, it circles the planet in the opposite direction from most moons.

What is Neptune like?

Neptune has a similar make-up to its twin planet, Uranus. It has an atmosphere made up mainly of hydrogen, together with some helium. Beneath this there is a huge, deep, hot ocean of water and liquid gases, including methane. In the centre, there is a core of rock, which may be about the same size of Earth.

When did Voyager 2 visit Neptune?

Neptune was the last planet Voyager2 visited on its 12 – years journey. Launched in 1977, Voyager 2 passed about 5,000 kilometres above Neptune cloud tops on August 24, 1989 – close than to any other planet. By then, it was more than 4,000 million kilometres from Earth, and its radio signals too more than four hours to get back.

Who found Pluto?

United States astronomer Percival Lowell built his own observatory, and led a search for a ninth planet. An astronomer who worked there, Clyde Tombaugh, finally discovered it in 1930.

What do we know about Pluto?

We do not know much about Pluto because it is so far away. At the furthest, it travels more than 7,000 million kilometres from the Sun. Even in powerful telescope, it looks only like a faint star. So far, no space probes have visited the planet. All we know is that Pluto is a deep – frozen ball of rock and ice. It probably has a covering of ‘snow’, made up of frozen methane gas.

What is special about Charon?

Pluto’s only a moon, Charon, is a unique in the Solar System, as it is half as big across as Pluto itself. No other moon is as big compared with its planet. Also, circles Pluto in the same time it takes Pluto to spin round once. This makes Charon appear fixed in the Pluto’s sky.

What would Charon look like from Pluto?

Because it appears fixed in Pluto’s sky, Charon can only be seen from one side of the planet. From that side, Charon would appear huge, much bigger than the Moon does on Earth. This is because Charon circles very close to Pluto, only about 20,000 kilometres away. Our Moon circles 20 times further from us.

NEPTUNE DATA

Diameter at equator : 49,500 million km

Average distance from Sun : 4,500 million km

Minimum distance from earth : 4,300 million km

Turns on axis : 17 hours 6 minutes

Circles Sun : 165 Earth-years

Temperature at cloud tops : -210°C

Satellites : 8


PLUTO DATA

Diameter at equator : 2,250 km

Average distance from Sun : 5,900 km

Minimum distance from earth : 4,300 km

Turns on axis : 6 Earth-days 9 hours

Circles Sun : 248 Earth- years

Surface temperature : -230°C

Satellites : 1